A NEW MECHANISM OF H2B=NH2 FORMATION IN THE REACTION OF B2H6 WITH NH3

The mechanisms of the reactions of diborane with ammonia have been investigated by ab initio molecular orbital methods. The activation barrier of the formation of aminoborane, H2B=NH2, from the adduct, H3B:NH3, of borane and ammonia is high (over 40 kcal/mol), because it is a reaction essentially forbidden by the Woodward-Hoffmann rule. A new cyclic transition state is found in the aminoborane formation mechanism. The barrier for this cyclic transition state is about 17 kcal/mol from the isolated diborane and ammonia at the MP4/6-31 G(d, p)//MP2/6-31G(d, p) + ZPE level.